1. Field of the Disclosure
The invention relates to an optical system and a display apparatus and more particularly relates to an illumination system and a projection apparatus.
2. Description of Related Art
Recently, projection apparatuses featuring solid-state light sources such as light-emitting diode (LED) and laser diode have gradually become dominant in the market. The light-emitting efficiency of the laser diode is about 20% in comparison with the normal LED; in order to remove the limitation on the LED light source, phosphor has been excited by the laser light source, and thereby the pure color light source required by the projector is generated. In a laser projection apparatus, the laser light source not only excites the phosphor to emit light but also acts as the direct light source which provides illumination to the projector. Besides, the number of the light sources may be adjusted in response to the requirement for brightness, so as to comply with different demands of various projectors for brightness. Accordingly, the projector with a laser light source system has great potential to replace the conventional high-pressure mercury lamp and become the next-generation mainstream projector.
In a conventional laser projector, laser beams emitted by laser emitters arranged in an array are collected onto a phosphor layer to output sufficient fluorescent brightness. However, the light spot resulting from the semiconductor laser emitters is about elliptic-shaped, and the light intensity distribution of the laser beam is similar to Gaussian distribution. By contrast, after the laser beam excites the phosphor, the light spot of the resultant beam is about circular-shaped, and the light intensity distribution of the excited beam is similar to Lambertian distribution. When the laser beam and the beam obtained by exciting the phosphor are combined, different shapes of the light spots and different light intensity distributions result in uneven illumination, such that the color of the displayed image projected by the laser projector is not uniform.
The light spot generated by the laser beam with the light intensity distribution being similar to Gaussian distribution has strong light intensity at the central unit area, such that the conversion efficiency of the phosphor is saturated and difficult to be improved, and thus the brightness of the displayed image projected by the laser projector isn't further enhanced. Besides, the light spot with high light intensity burns the phosphor or reduces the service life of the phosphor.
Taiwan Patent Publication no. 201235618 discloses a light source apparatus with an excitation light source. U.S. Pat. No. 8,109,638 discloses a projector. U.S. Pat. No. 6,870,650 discloses that the diffusion angle of the laser beam is different in the horizontal direction and in the perpendicular direction after the laser beam passes through a diffusion sheet. U.S. Pat. No. 7,271,962 discloses an image formation apparatus.